Method of coded data storage by means of coded inks in which the code components have particular absorption bands in the infrared

ABSTRACT

A data storage method is described in which inks with code components of compounds having narrow absorption bands in the infrared are impressed on a substrate which is transparent to the infrared in the regions of the absorption bands of the code components. Decoding is effected by passing infrared radiation through the areas of the substrate where the symbols have been placed in the coded inks and the infrared radiation detected in the particular bands of the coded components to produce electrical signals which are then analyzed to produce a readout corresponding to the particular symbol.

United States Patent Inventor Leslie C. Lane, Jr.

Stamford, Conn.

Appl. No. 777,538

Filed Sept. 25, 1968 Patented Feb. 23, 1971 Assignee American CyanamidCompany Stamford, Conn.

Continuation-impart of Ser. No. 526,183, Feb. 9, 1966, now abandonedMETHOD OF CODED DATA STORAGE BY MEANS OF CODED INKS IN WHICH THE CODECOMPONENTS HAVE PARTICULAR ABSORPTION Pn'mary Examiner-Archie R,Borchelt Attorney Samuel Branch Walker ABSTRACT: A data storage methodis described in which inks with code components of compounds havingnarrow absorption bands in the infrared are impressed on a substratewhich is transparent to the infrared in the regions of the absorptionbands of the code components. Decoding is effected by passing infraredradiation through the areas of the substrate where the symbols have beenplaced in the coded inks and the infrared radiation detected in theparticular bands of the coded components to produce electrical signalswhich are then analyzed to produce a readout corresponding to theparticular symbol.

pmmm'rmzsml 3.566120 READOUT INVENTOR. LESLIE 6'. LANE JR.

BY W W M ATTORNEY METHOD OF CODED DATA STORAGE BY MEANS OF CODED INKS INWHICH THE CODE COMPONENTS HAVE PARTICULAR ABSORPTION BANDS IN THEINFRARED REALTED APPLICATIONS This application is a continuation-in-partof my earlier application, Ser. No. 526,183, filed Feb. 9, 1966, and nowabandoned.

BACKGROUND OF THE INVENTION In the patent of Freeman and Halverson, US.Pat. No. 3,473,027, Oct. 14, 1969, there is described a method andapparatus for recording and retrieving information by means ofphotoluminescent materials. In the patent so-called coded inks areutilized in which various symbols, such as numbers, are represented bythe presence or absence of particular photoluminescent material ratherthan representing the symbols by particular shapes which aredistinguishable either visually, magnetically or by othercharacteristics. When dealing with numbers, for example, four differentphotoluminescent materials may be used, and this gives the possibilityof 15 different codes, the general formula being 2" l. Larger numbers ofcoded materials permit representing still larger numbers of differentsymbols. For example, with six different photoluminescent materials 63symbols are distinguishable. The different coded inks contained'thenecessary mixtures of materials which fluoresced under ultravioletillumination in definite colors.

SUMMARY OF THE INVENTION The present invention provides symbols whichhave one or more components having sharp absorption bands in theinfrared. The choice of materials is wide, as most transparent organiccompounds have one or more sharp absorption bands in the infrared. Thesubstrate on which the symbols are written or printed must, of course,transmit infrared at least in the ranges in which the absorption bandsof the components are located. This is, however, no problem as there areplastics, such as for example polyethylene, which are transparent to theinfrared through a wide range. As-most of the infrared absorbers arecolorless or transparent, the symbols are not visible to the eye, andtherefore any message is secret. Of course the same advantages as withfluorescent materials are shared, namely that the symbol can be readregardless of its shape and is, therefore, machine readable even ifsomewhat mutilated.

For certain purposes it is desirable that the symbols be readable undervisible light. This can be effected in the present invention byintroducing a'small amount of a suitable dyestuff in the coded inks Ofcourse the colorant used must be on which has reasonable transmission inthe ranges of infrared in which the absorption bands of the symbolcomponents are located and does not have itself sharp absorption bandsin these ranges which would interfere 'with recognition of the symbolsthemselves.

In readout out or retrieving the information according to the presentinvention, an infrared source shines on the transparent or translucentsubstrate containing the symbols, the source radiating over asufficiently wide infrared band to include all of the strong absorptionbands of the different components of the symbols. n the other side ofthe transparent substrate are located a series of light pipes, which maybe suitable plastic rods, glass fiber bundles, and the like. The end ofeach light pipe carries the radiation through a narrow band filter to aradiation detector, one for each component. The filter corresponds tothe absorption band of the particular component and is preferably narrowband, but this presents no problem with modern narrow band filters, suchas interference filters. It goes without saying that the light pip esmust be capable of transmitting radiation in the proper wavelengths inthe infrared where the components have strong absorption bands.

It will be found that there are a large number of compounds, such asorganic plastics, with bands located in the near infrared, for examplewavelengths shorter than 3a, so that glass fiber light pipes can beemployed. lf components having absorption bands in the further infraredare used, the light pipes must of course be modified accordingly. Fibersor rods of different plastics or even a hollow pipe with its innersurfaces in the form of a good infrared mirror can be used. When fiberor rod light pipes are used of particular plastics, these may be thesame plastics as the substrate, or a different component.

Typical materials are polymethylmethacrylate, polyacrylamide, polyvinylalcohol; various amides and polyamides, such as N,N-dialkyl amides;super polyamides, such as for example nylon-6, which is a polymer ofw-amino caproic acid, and the like. Many of these components are notreadily soluble in solvents such as benzene, toluene, cyclohexane, andthe like which do not exhibit bands that conflict with the absorptionbands of the components. In such cases finely divided powders may bedispersedin inks having a film-forming substance which also does nothave absorption bands in the infrared which conflict with the bands ofthe components. Such inks normally require a film-forming substance, forwhich polyolefins are suitable, for example solid polyisobutylene. Ofcourse all of the various components can be distributed in inks in thisform even through some of them, such as polymethylmethacrylate, arereadily soluble in suitable solvents.

The amounts of the components are not critical, but they must besufficient in the residue form when the volatile solvents of the inksevaporate so that the components are represented by a layer of atleast'20 to 50 microns.

Radiation detectors may be of conventional types for use in infrared.For example, if all of the components or some of them are in the verynear infrared, it is possible to use special photomultiplier tubes, andwhere this is feasible it constitutes an advantage, as the sensitivityof the photomultiplier tube is so great that amplification of the signalfrom the tube can often be dispensed with. In other ranges inthe-infrared, it is necessary to use a different type of radiationdetector, which may be either photoresistive or photovoltaic. Forexample, a lead sulfide or lead selenide cell.

Some of the typical components, such as polymethylmethacrylate; nylon-6;or N,N-dialkyl amides, such as N,N- dibutylpropionamide; andpolyacrylonitrile have infrared absorption bands at wavelengths longerthan 4p. and ranging up to slightly over 6;; for some of the amides,such as nylon-6. In suchcases it is possible to use a photoresistivedetector, such as indium antimonide.

lt.is also possible to use thermal detectors, such as thermocouples orthermopiles, thermistors and the like, which are of course responsivethrough very wide ranges of the infrared. In the case of these detectorswhich are less sensitive, it is normal to provide signal amplificationand standard preamplifiers, such as for example solid statepreamplifiers, are used. As the nature of the detector and/or theamplification of its signal are not changed by the present invention, itis not desired to limit it to any particular design.

The signals from the various radiation detectors are then read out instandard readout circuits, which also are not changed by the presentinvention and which can be the same as are used in the readout of theFreeman and Halverson patent above referred to. One may consider thatthe novelty of the present invention ceases when signals are producedfrom the various radiation detectors, and it is an advantage of theinvention that no new design of detectors, amplifiers or readoutcircuitry is required.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows in diagrammatic forman apparatus for reading a code containing four components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS ln the drawing an infrared lampof conventional design 1, which radiates infrared in the range in whichall of the components have absorption bands, shines infrared onto asubstrate 2 which is transparent to infrared and may, for example, bepolyethylene. On this substrate there are printed various symbols: A, B,C, and D, which for simplicity are shown as containing a singlecomponent only, though'of course any particular symbol may have two,three or four components. The thickness of the symbols is enormouslyexaggerated for clearn'ess and in actual fact they are no thicker thanordinary printing.

As a typical illustration, component A is polymethylmethacrylate with aninfrared absorption band at.5.8,u, B is nylon-6 orN,N-dibutylpropionamide with an infrared absorption band at about 6.1a,C is polyacrylonitrile with an absorption band at 4.4;/., and D ispolyvinyl alcohol with an absorption band at 2.96p.. If separate inksare used for each component, component A can be a benzene solution ofthe polymer, but the other three components are not readily soluble insuitable solvents and therefore in the form'of very finely dividedpowder uniformly dispersed in an ink which is a solution of solidpolyisobutylene in eyclohexane. Of course if inks are used witha numberof components mixed in them, it is preferable to have thepolymethylmethacrylate also in the form of a fine powder. While thethickness of the symbols is exaggerated, the layer of the componentmaterial should be at least 20p. to 50p. in thickness. 1

The entrance pupil of the infrared source after the radiation has passedthrough the substrate 2 passes through a field lens 3 which focuses theentrance pupil onto a plane in which four light pipes 4A, 4B, 4C, and 4Dare located. The light pipes are capable of transmitting infraredradiation in the range including the strong absorption band of theparticular components respectively. The entrance of the light pipes isshown with the pipes quite widely separated for clarity. In an actualdevice they are of course quite closely adjacent, which is made possibleby the fact that the pipes can be bent to bring the radiation out into awider area. The radiation from each light pipe passes through a sharpcutting infrared filter 5A, 5B, 5C, and 50 respectively, each filterpassing only the wavelength range corresponding to the absorption bandof a particular component or a little beyond, the filters being arrangedso that there is no overlap in transmission. Back of the filters 5A toSD are four radiation detectors shown diagrammatically as 6A, 6B, 6C,and 6D. The detectors may be of indium antimonide or of coursethermopiles or thermistor bolometers with suitable amplification to makeup for the lower sensitivity of these detectors. With components whichhave absorption bands in the sufficiently short wave infrared, infraredsensitive photomultiplier tubes may be used as the detectors and havethe advantage of enormously enhanced sensitivity.

Each radiation detector produces an electrical signal if its particularcomponent is absent but produces no signal if it is present, althoughthe reverse effect can be achieved by Chang ing the electronics. Theelectrical signals from the detectors pass into an amplifier and readoutcircuitry 7 of the conventional design which reads out the particularsymbols. This element is of conventional design and may be amultichannel analyzer, an oscilloscope with timing so that each signalappears at a particular point of the horizontal sweep, or any otherstandard form of readout circuit. Since it is an advantage of thepresent invention that any known circuit may be used and the inventionis not limited to any particular design, this element is shown in thedrawings as a block.

The preferred modification of the invention using light pipes andspatially separated filtering means and detector is not the only form inwhich the present invention can be developed. Where solid state infrareddetectors are used, such as indium antimonide, these canv be very tinyand provided with equally small filters, the detectors being arranged inthe form of a mosaic on which the field lens ima es the infrared beamafter passing through any particular co ed symbol. The

signals from the different detectors pass to preamplifiers and thereadout circuit in the conventional manner. Very small apparatus is thusmade possible and for certain uses this compactness is of primaryimportance. However, the modification described in the drawing usinglight pipes and more widely separated filters and radiation detectorspermits using a wider choice of detectors, including some of higherefficiency, such as for example photomultiplier tubes, where theabsorption band of a particular component is the sufficiently short waveinfrared. Therefore, the modification described in the drawing usinglight pipes is preferred, but the invention is in no sense limitedthereto.

I claim:

1. In a process for encoding and retrieval of information in which theencoding is with coded inks having various components, the codeconstituting the absence of presence of particular components torepresent a symbol, the improvement which comprises:

a. applying to a substrate transparent to infrared radiation symbolsencoded in inks having various components with narrow absorption bandswithin the wavelength range in the infrared in which the substrate istransparent;

b. shining infrared radiation in the wavelength range containing thenarrow absorption bands through the substrate, detecting radiationencountering the coding components by infrared detectors, each detectorbeing responsive to wavelength in the infrared including the absorptionband of a coding component and being unresponsive to wavelengths in therange of absorption of the other components, the detectors transforminginfrared radiations into an'electrical signal; and

c. transforming said signal into a readout of a coded symbol representedby the presence and absence of the coding components.

2. A process according to claim 1 comprising focusing the infraredradiation passing through the ink component on the substratecorresponding to a symbol onto a fixed plane and conducting saidradiation to each detector individually.

3. A process according to claim 2 in which the individual detectors arein the plane and receive infrared radiation directly,

1. In a process for encoding and retrieval of information in which theencoding is with coded inks having various components, the codeconstituting the absence of presence of particular components torepresent a symbol, the improvement which comprises: a. applying to asubstrate transparent to infrared radiation symbols encoded in inkshaving various components with narrow absorption bands within thewavelength range in the infrared in which the substrate is transparent;b. shining infrared radiation in the wavelength range containing thenarrow absorption bands through the substrate, detecting radiationencountering the coding components by infrared detectors, each detectorbeing responsive to wavelength in the infrared including the absorptionband of a coding component and being unresponsive to wavelengths in therange of absorption of the other components, the detectors transforminginfrared radiations into an electrical signal; and c. transforming saidsignal into a readout of a coded symbol represented by the presence andabsence of the coding components.
 2. A process according to claim 1comprising focusing the infrared radiation passing through the inkcomponent on the substrate corresponding to a symbol onto a fixed planeand conducting said radiation to each detector individually.
 3. Aprocess according to claim 2 in which the individual detectors are inthe plane and receive infrared radiation directly.